The present invention relates to a clamping device for connecting flanged through sections of support structures, particularly for mine supports.
Clamping devices of the type under discussion are known. One of such device is disclosed, for example in DE-OS No. 2,850,350. Such a clamping device includes an upper stirrup, a lower stirrup and clamping bolts. In this conventional clamping device clamping bolts are utilized, the heads of which are formed so that they are laterally offset relative to the axes of the bolts towards the free ends of the flanges of the stirrups. The back side of the bolt head of each bolt, facing to the through sections being clamped, extends in the plane of the axis of the bolt. The underside of the head of each bolt lies substantially flush on the flat upper side of the flange of the stirrup. The transition zones between the underside of the bolt head and its back side are convexly curved and are supported in a form-locking manner in the shaped transition regions between the lateral web of the stirrup and its flange. The transition portions between the shaft of the bolt and the underside of its head is sharp-edged and extends vertically. The back side of the bolt shaft, facing the through sections being clamped, extends upwardly up to the plane which is parallel to the end face of the head of the bolt.
The upper stirrup, the lower stirrup and clamping bolts of the clamping device are adjusted to each other so that the head of each bolt smugly lies on the upper stirrup not only in a non-clamped position but also when a certain clamping force is applied to each bolt.
When the clamping force, applied to the clamping bolt, exceeds a predetermined value, particularly when rock pressure is exerted on the mine support, the known clamping device can be subjected to such loads that the free ends of the stirrups can bend in the direction towards the clamping nuts tightening the clamping bolts. Thereby contact surfaces between the heads of the bolts and the upper stirrup are reduced, which results in increase of contact pressures. These high contact pressures are concentrated in the narrow region around the through opening formed in the upper stirrup for passing therethrough of the clamping bolt. Immediate edge region of the opening is therefore extremely highly loaded. This loading is further increased because the portions of the bolt heads, protruding from the bolt shafts in the direction of elongation of the through sections of the support structure, bend towards the end faces of the bolt heads. The highest forces must be transmitted by relatively small contact surfaces. Such extremely high load concentration at the edges of the through openings can easily lead to a premature failure of the whole clamping device so that the upper stirrup would tear up in the region of the opening, or the bolt head would pass through that opening.
Efforts have been made to make the upper stirrup of such material to make the whole clamping device satisfactory. Further material cost reductions have resulted in that the curved regions between the lateral webs of the upper stirrup and its flanges have weakened. However, practically, a material layout in the known device has been a comparatively weak system. This led to the fact that when rock pressures were exerted on the structural components of the clamping devices of the mine supports all the components were subject to considerable deformations. This in turn caused plays between the elements clamped to each other. This effect led eventually to premature malfunctions of each individual mine arch support.